Method and apparatus for cellular handovers involving sidelink communications

ABSTRACT

In one aspect of the teachings herein, a radio network node (20) associated with a source cell (22-1) provides sidelink configuration information to a wireless device (16) to be handed over to a target cell (22-2). The information indicates the sidelink synchronization and resource configurations associated with the target cell, and the wireless device performs sidelink communications based on the sidelink synchronization and resource configurations of the target cell. Receiving the sidelink resource and timing information associated with the target cell enables the wireless device to perform sidelink communications using the target-cell resources and timing, even while still being served in a cellular sense from the source cell. Thus, the wireless device may begin or resume sidelink communications using the sidelink timing and resources associated with the target cell, irrespective of whether cellular handover of the wireless device from the source cell to the target cell has completed.

TECHNICAL FIELD

The present invention relates to cellular handovers in a wirelesscommunication network, such as from a source cell to a target cell, andparticularly relates to cellular handovers involving sidelinkcommunications.

BACKGROUND

The term “sidelink” refers to a direct radio link for communicationamong devices in Third Generation Partnership Project (3GPP) radioaccess networks, as opposed to communication via the cellularinfrastructure (uplink and downlink). The sidelink is also referred toas a Device-to-Device (or D2D) link. The term “V2x” denotes“Vehicle-to-Everything” communications, and it encompassescommunications involving vehicles as message sources or destinations.V2x communications may involve respective vehicles as endpoints or mayinvolve vehicles communicating with infrastructure nodes or other typesof devices. The “PC5” interface is used to carry V2x communicationsbetween user equipments (UEs), which may be embedded in vehicles orother node, device, or system types engaged in Proximity Services(ProSe) D2D communications. The interested reader may refer toR3-150744—ProSe Resource Coordination Across eNBs, Ericsson,R3-132277—Mobility for D2D UEs, Ericsson, and 3GPP TS 36.423 Rel-13, foradditional context.

Release 12 of the 3GPP specifications extend the LTE standard with D2Dor sidelink communication features targeting both commercial and PublicSafety applications. Some applications enabled by Rel-12 LTE are devicediscovery, where devices are able to sense the proximity of anotherdevice and associated application by broadcasting and detectingdiscovery messages that carry device and application identities. Anotherapplication consists of direct communication based on physical channelsterminated directly between wireless devices. Here, the term “device”means a UE or essentially any apparatus configured for sidelinkcommunications.

One of the potential extensions for the D2D work consists of support ofV2x communication, which includes any combination of directcommunication between vehicles, pedestrians and infrastructure. V2xcommunication may take advantage of a network (NW) infrastructure, whenavailable, but at least basic V2x connectivity should be possible evenin case of lack of coverage. Providing an LTE-based V2x interface may beeconomically advantageous because of the LTE economies of scale and itmay enable tighter integration between communications with the NWinfrastructure (V2I) and V2P and V2V communications, as compared tousing a dedicated V2x technology. The nearby figure illustrates exampleV2x scenarios for an LTE-based wireless communication network.

V2x communications may carry both non-safety and safety information,where each of the applications and services may be associated withspecific requirements sets, e.g., in terms of latency, reliability,capacity, etc. ETSI has defined two types of messages for road safety:Cooperative Awareness Message (CAM) and Decentralized EnvironmentalNotification Message (DENM).

CAM messages are intended to enable vehicles, including emergencyvehicles, to notify their presence and other relevant parameters in abroadcast fashion. Such messages target other vehicles, pedestrians, andinfrastructure, and are handled by their applications. CAM message alsoserves as active assistance to safety driving for normal traffic. Theavailability of a CAM message is indicatively checked for every 100 ms,yielding a maximum detection latency requirement of <=100 ms for mostmessages. However, the latency requirement for Pre-crash sensing warningis 50 ms.

DENM messages are event-triggered, such as by braking, and theavailability of a DENM message is also checked for every 100 ms, and therequirement of maximum latency is <=100 ms.

The package size of CAM and DENM message varies from 100 plus to 800plus bytes and the typical size is around 300 bytes. The message issupposed to be detected by all vehicles in proximity.

The SAE (Society of the Automotive Engineers) also defined the BasicSafety Message (BSM) for DSRC with various messages sizes defined.According to the importance and urgency of the messages, the BSMs arefurther classified into different priorities.

UE mobility—i.e., cellular mobility within a cellular network—can besupported for UEs that are using PC5 resources. When such a UE is handedover, the PC5 resources with which it has been configured by its servingcell can be included by the source eNB in its “RRC context” (defined asRRC Context IE by 3GPP TS 36.423 and TS 36.331), signaled to the targeteNB in the X2 HANDOVER REQUEST message. If the target cell is able toallocate the same set of radio resources to the UE, this prevents the UEfrom losing the PC5 connection. However, it is recognized herein thatthe UE still may experience unacceptably long interruptions in itssidelink communications during cellular handovers.

In typical D2D scenarios, PC5 synchronization in conjunction withcellular mobility may not be an issue due to the less stringent mobilityrequirements with respect to e.g. V2x, where high UE mobility istypical. As previously mentioned sidelink transmissions (also known asD2D or ProSe) in cellular spectrum that have been standardized in 3GPPsince Rel-12 can be tailored for V2X-type services. In 3GPP Rel-12 twodifferent operative modes have been specified in 3GPP. In one mode, a UEin RRC_CONNECTED mode requests D2D resources and the eNB grants them viaPDCCH (DCIS) or via dedicated signaling. In another mode, a UEautonomously selects resources for transmission from a pool of availableresources that the eNB provides in broadcast via System InformationBlock (SIB) signaling for transmissions on carriers other than the PCellor via dedicated signaling for transmission on the PCell. Therefore,unlike the first operation mode, the second operation mode can beperformed also by UEs in RRC_IDLE.

A key issue recognized in this disclosure is that V2x traffic ischaracterized by messages with certain latency constraints. During acellular handover of a UE there is typically some increase in latencydue to the fact that a UE needs to read system information for thecellular network and perform a resynchronization and RRC reconfigurationto the target cell before being able to resume communication operations.Such operations may be regarded as performing a cellular handoverprocess. The latency associated with the cellular handover process mayviolate some V2x traffic latency constraints.

SUMMARY

In one aspect of the teachings herein, a radio network node associatedwith a source cell provides sidelink configuration information to awireless device to be handed over to a target cell. The informationindicates the sidelink synchronization and resource configurationsassociated with a target cell, and the wireless device performs sidelinkcommunications based on the sidelink synchronization and resourceconfigurations of the target cell. Receiving the sidelink resource andtiming information associated with the target cell allows the wirelessdevice to perform sidelink communications using the target-cellresources and timing, even while still being served in a cellular sensefrom the source cell. Thus, the wireless device may begin or resumesidelink communications using the sidelink timing and resourcesassociated with the target cell, irrespective of whether cellularhandover of the wireless device from the source cell to the target cellhas completed.

In an example embodiment, a method of operation in a wireless deviceconfigured for operation in a wireless communication network includesthe device receiving sidelink configuration information for a secondcell. The received information indicates sidelink resources and sidelinktiming associated with the second cell, and the method further includesthe device receiving handover signaling indicating a cellular handoverof the wireless device from a first cell to the second cell. In responseto receiving the handover signaling, the device performs a cellularhandover process with respect to the second cell, including acquiringcellular synchronization with respect to the second cell, and performs asidelink synchronization process with respect to the second cell. Thesidelink synchronization process includes acquiring sidelink timingsynchronization with respect to the second cell, and the method furtherincludes the wireless device resuming or initiating sidelinkcommunications using the sidelink resources and the sidelink timingassociated with the second cell, once sidelink synchronization isacquired with respect to the second cell via the sidelinksynchronization process and irrespective of whether the cellularhandover process has been completed.

In a related example embodiment, a wireless device configured foroperation in a wireless communication network includes communicationcircuitry and processing circuitry. The communication circuitry isconfigured for communicating with radio network nodes in the wirelesscommunication network via cellular connections and for communicatingwith other wireless devices or nodes via sidelink connections.

The processing circuitry is operatively associated with thecommunication circuitry and configured to receive sidelink configurationinformation for a second cell of the wireless communication network,indicating sidelink resources and sidelink timing associated with thesecond cell, and to receive handover signaling indicating a cellularhandover of the wireless device from a first cell of the wirelesscommunication network to the second cell. Further, the processingcircuitry is configured to perform a cellular handover process and asidelink synchronization process, in response to receiving the handoversignaling.

The cellular handover process is performed with respect to the secondcell and includes acquiring cellular synchronization with respect to thesecond cell. The sidelink synchronization process is performed withrespect to the second cell and includes acquiring sidelink timingsynchronization with respect to the second cell. Further, the processingcircuitry is configured to resume or initiate sidelink communicationsusing the sidelink resources and the sidelink timing associated with thesecond cell, once sidelink synchronization is acquired with respect tothe second cell via the sidelink synchronization process andirrespective of whether the cellular handover process has beencompleted. That is, the sidelink synchronization process may becompleted before the cellular synchronization process completes, andacquiring sidelink synchronization via the sidelink synchronizationprocess allows the wireless device to resume or initiate sidelinkcommunications using resources and timing associated with the secondcell before completion of the cellular handover process.

In another example embodiment, a method of operation at a radio networknode configured for operation in a wireless communication networkincludes obtaining sidelink configuration information for a second cellthat neighbors a first cell provided by the radio network node. Thesidelink configuration information indicates a sidelink resourceconfiguration for the second cell, and a sidelink synchronizationconfiguration for the second cell, and the method further includestransmitting the sidelink configuration information to a wireless devicehaving a cellular connection to the first cell, in advance of, or inconjunction with, a cellular handover of the wireless device from thefirst cell to the second cell. Providing the sidelink configurationinformation to the wireless device enables the wireless device toacquire sidelink timing synchronization with respect to the second cell.

In a related embodiment, a radio network node is configured foroperation in a wireless communication network and includes communicationcircuitry and processing circuitry. The communication circuitrycomprises receiver and transmitter circuitry configured at least forcommunicating with wireless devices, and the processing circuitry isoperatively associated with the communication interface circuitry andconfigured to perform a number of operations. In a particular example,the processing circuitry is configured to obtain sidelink configurationinformation for a second cell that neighbors a first cell provided bythe radio network node, where the sidelink configuration informationindicates a sidelink resource configuration for the second cell, and asidelink synchronization configuration for the second cell. Theprocessing circuitry is further configured to transmit the sidelinkconfiguration information to a wireless device having a cellularconnection to the first cell, in advance of, or in conjunction with, acellular handover of the wireless device from the first cell to thesecond cell. The sidelink configuration information enables the wirelessdevice to acquire sidelink timing synchronization with respect to thesecond cell.

Of course, the present invention is not limited to the above featuresand advantages. Indeed, those skilled in the art will recognizeadditional features and advantages upon reading the following detaileddescription, and upon viewing the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of one embodiment of a wireless communicationnetwork.

FIG. 2 is a signal flow diagram of one embodiment of signalingassociated with a handover in a cellular network that involves sidelinkcommunications.

FIG. 3 is a block diagram of example embodiments of a severalcommunication nodes, including a wireless device, a radio network node,and a core network node.

FIG. 4 is a logic flow diagram of one embodiment of a method ofprocessing at a wireless device, for a cellular handover of the wirelessdevice involving sidelink communications.

FIG. 5 is a logic flow diagram of one embodiment of a method ofprocessing at a radio network node, for cellular handover of a wirelessdevice involving sidelink communications.

DETAILED DESCRIPTION

By way of non-limiting example, FIG. 1 illustrates one embodiment of awireless communication network, such as a wide-area cellular radionetwork based on the Long Term Evolution (LTE) standard or based onanother Third Generation Partnership Project (3GPP) standard.

The network 10 includes a Radio Access Network or RAN 12, along with aCore Network or CN 14. The network 10 communicatively couplesessentially any number of wireless devices 16 (WDs in the diagram) toeach other, or to any number of other systems or devices reachablethrough one or more external networks 18. Only six WDs 16 (16-1 through16-6) are shown by way of example, but it shall be understood thatpotentially many more WDs 16 may be operating in the network 10. Itshall also be understood that the WDs 16 are not necessarily all of thesame type or function. Example WDs 16 include any one or more ofsmartphones, feature phones, wireless computers, communication networkadaptors, dongles, Machine-Type Communication (MTC) devices, alsoreferred to as M2M devices, etc. Using 3GPP parlance, the WDs 16 may bereferred to as UEs or “user equipments”.

The RAN 10 includes a number of base stations 20, such as eNBs in theLTE context. The base stations are a type of radio network node and aremore generally referred to as radio network nodes 20. In the diagram,each radio network node 20 provides a cell 22, e.g., the network node20-1 provides the cell 22-1, and so on. As an example, a cell 22 may beregarded as comprising specific communication resources—e.g., specificfrequencies and/or times—used for providing network coverage over acorresponding geographic area. Of course, there may be overlapping cells22, and a given network node 20 may provide more than one cell 22.

The resources—e.g., radio resources—allocated for sidelinkcommunications may be associated with the cellular radio resources onthe Uplink (UL). To carry out sidelink communications using suchresources, a given WD 16 must know the corresponding sidelink resourceconfiguration and sidelink synchronization configuration. For example,the WD 16-6 may perform sidelink communications using sidelink timingand resource configurations associated with the cell 22-2, while the WD16-1 performs sidelink communications using the sidelink timing andresource configurations associated with the cell 22-1. It should beunderstood that such sidelink communications may involve other WDs 16depicted in the figure, or may involve other nodes or devices, etc., notexplicitly shown.

Consider a non-limiting example scenario where the WD 16-1 has acellular connection to the base station 20-1/cell 22-1, and is carryingout sidelink communications using sidelink timing and resourceconfigurations associated with the cell 22-1. According to an exampleembodiment herein, in advance of, or in conjunction with, handover ofthe WD 16-1 to the cell 22-2, the base station 20-1 sends sidelinkconfiguration information to the WD 16-1, indicating a sidelinksynchronization configuration (sidelink timing), and a sidelink resourceconfiguration associated with the cell 22-2. The WD 16-1 uses theindicated configuration information to carry out a sidelinksynchronization process, whereby it acquires sidelink synchronizationwith respect to the cell 22-2. Once synchronized with respect tosidelink communications via the sidelink synchronization process, the WD16-1 resumes or begins sidelink communications using the sidelinkresources and timing associated with the cell 22-2.

Advantageously, according to such operation, the WD 16-1 begins orresumes sidelink communications using the timing and resourcesassociated with the cell 22-2 irrespective of whether the WD 16-1 hascompleted cellular handover processing with respect to the cell 22-2.For example, the WD 16-1 may be able to acquire sidelink synchronizationmore quickly than it can acquire cellular synchronization, whichinvolves cell synchronization using cellular synchronization signals onthe downlink and the acquisition of system information (SI) forconnecting to the cell 22-2. More broadly, the WD 16-1 may performsidelink communications using the sidelink timing and resourceconfiguration of the cell 22-2 while still being served in the cellularsense by the cell 22-1, or at least before completing cellular handoverto the cell 22-2.

FIG. 2 illustrates an example embodiment of such processing, involving aWD 16-1 engaged in sidelink communications with another WD 16-2. Atarget radio network node (RNN) 20-2 sends sidelink configurationinformation to a source RNN 20-1. The sidelink configuration informationcomprises, for example, sidelink resource configuration informationindicating the configuration of resources allocated for sidelinkcommunications in a target cell 22-2 associated with the target RNN20-2. The sidelink configuration information may also include sidelinksynchronization configuration information for the target cell 22-2,which information may indicate the time base or reference used forsynchronizing sidelink communications to the target cell 22-2.

The source RNN 20-1 is associated with a source cell 22-1 and it may beassumed that the WD 16-1 is to be handed over from the source RNN20-1/source cell 22-1 to the target RNN 20-2/target cell 22-2, and thatsuch handover is undertaken while the WD 16-1 is engaged in sidelinkcommunications with another WD 16-2. Before handover is performed, thesidelink communications use source-cell resources and timingsynchronization, and it shall be understood that the source and targetRNNs 20-1 and 20-2 may be, for example, eNBs associated with respectivecells.

The WD 16-1 has a cellular connection to the RNN 20-1, e.g., as a“serving” node for the WD 16-1, and source RNN 20-1 may use thatcellular connection to provide the WD 16-1 with sidelink configurationinformation for the target cell 22-2, e.g., by sending sidelink resourceconfiguration information and sidelink synchronization configurationinformation to the WD 16-1. While FIG. 2 suggests the possibility ofsuch information as being sent separately from the handover signaling,e.g., in advance of the handover signaling sent from the RNN 20-1 to theWD 16-1, it shall be understood that such signaling may be carriedwithin the handover signaling. Broadly, the source RNN 20-1 sendssidelink configuration information for the target cell 22-2 inconjunction with handing the WD 16-1 over from the source cell 22-1 tothe target cell 22-2, where such handover operations involve the sourceRNN 20-1 sending handover signaling to the target RNN 20-2, and to theWD 16-1.

The WD 16-1 acquires sidelink synchronization with the target cell 22-2using the synchronization configuration information received from thesource RNN 20-1 for the target RNN 20-2/target cell 22-2, and resumessidelink communication with the other WD 16-2, using the target-cellresources and synchronization. In this example, such resumption occursbefore completion of the cellular handover process, which involves theWD 16-1 synchronizing in a cellular sense to the target RNN 20-2,acquiring system information for the target RNN 20-2, and carrying out aRadio Resource Control (RRC) reconfiguration, for establishing acellular connection to the target RNN 20-2.

FIG. 3 illustrates example embodiments of a WD 16, a radio network node20, and a Core Network (CN) node 24. In an LTE example, the radionetwork node 20 may be an eNB, and the CN node 24 may be a MobilityManagement Entity (MME), an Operations and Maintenance (OAM) node, etc.

The radio network node 20 comprises a communication circuitry 30,processing circuitry 32, and storage 34. The communication circuitry 30comprises communication interface circuits configured for communicatingwith one or more WDs 16, one or more CN nodes, and one or more otherradio network nodes 20, and such circuitry may comprise separateinterfaces. For example, the communication circuitry 30 includes one ormore cellular radio circuits, such as a transceiver comprising areceiver circuit (RX) and a transmitter circuit (TX), along withassociated transmit and receive processing circuitry, for communicatingwith WDs 16. Further, the communication circuitry 30 includes a networkcommunication interface, e.g., an S1 interface, for communicating withthe CN node 24.

The processing circuitry 32 comprises fixed circuitry, programmedcircuitry, or a mix of fixed and programmed circuitry. In an exampleembodiment, the processing circuitry 32 comprises one or moremicroprocessor-based circuits or one or more DSP-based, FPGA-based, orASIC-based circuits, or any mix thereof. In a particular example, theprocessing circuitry 32 is specially adapted or otherwise configured tooperate according to the radio network node method(s) disclosed herein,via the execution of computer program instructions comprising a computerprogram 36. The processing circuitry 32 may further use and/or storevarious items of configuration data 38 associated with such operation,via the storage 34.

The storage 34 comprises any one or more of solid-state storage, diskstorage, etc., and may provide both volatile, working memory andnon-volatile, program and data storage. The storage 34, therefore, mayinclude a mix of memory or storage circuits or device types.Non-limiting examples include any one or more of SRAM, DRAM, FLASH,EEPROM, and Solid State Disk (SSD) storage.

In any case, it shall be understood that in one or more embodiments thestorage 34 includes a non-transitory computer-readable medium storing acomputer program 36, the execution of which by the processing circuitryin the radio network node 20 configures the processing circuitry 32according to the teachings herein. Non-transitory, as used here, doesnot necessarily mean permanent or unchanging, but does denote storage ofat least some persistence.

The radio network node 20 also may include a Global Navigation SatelliteSystem (GNSS) timing circuit 39, e.g., for synchronizing sidelinkcommunications with respect to its resources, based on GNSS timing.Alternatively, the radio network node 20 may receive GNSS timing fromanother node in the network 10.

Similarly, the WD 16 comprises communication circuitry 40, processingcircuitry 42, and storage 44. The communication circuitry 40 comprises,for example, one or more cellular radio circuits, such as a transceivercomprising a receiver circuit (RX) and a transmitter circuit (TX), alongwith associated transmit and receive processing circuitry. Thecommunication circuitry 40 may also include other types of communicationinterface circuitry, e.g., for near-field communications, Wi-Fi,Bluetooth, etc.

The processing circuitry 42 comprises fixed circuitry, programmedcircuitry, or a mix of fixed and programmed circuitry. In an exampleembodiment, the processing circuitry 42 comprises one or moremicroprocessor-based circuits or one or more DSP-based, FPGA-based, orASIC-based circuits, or any mix thereof.

In a particular example, the processing circuit 42 is specially adaptedor otherwise configured to carry out the device-side signaling andoperations disclosed herein, via the execution of computer programinstructions comprising a computer program 46. The processing circuitry42 may further use and or store various items of configuration data 48associated with such operation, via the storage 44.

The storage 44 comprises any one or more of solid-state storage, diskstorage, etc., and may provide both volatile, working memory andnon-volatile, program and data storage. Thus, the storage 44 may includea mix of memory or storage circuits or device types. Non-limitingexamples include any one or more of SRAM, DRAM, FLASH, EEPROM, and SolidState Disk (SSD) storage. It shall be understood that in one or moreembodiments the storage 44 includes a non-transitory computer-readablemedium storing a computer program 46, the execution of which byprocessing circuitry 42 in the WD 16 configures the processing circuitry42 according to the teachings herein.

The CN node 24 comprises communication circuitry 60, processingcircuitry 62, and storage 64. The communication circuitry 60 comprisescommunication interface circuits configured for communicating with oneor more radio network nodes 24, and, possibly, with one or more other CNnodes of like or differing types. The communication circuitry 60,therefore, may comprise separate interfaces, e.g., an S1 interface, forcommunicating with the radio network node 20, and one or more othertypes of interfaces for communication with other types of nodes.

The processing circuitry 62 comprises fixed circuitry, programmedcircuitry, or a mix of fixed and programmed circuitry. In an exampleembodiment, the processing circuitry 62 comprises one or moremicroprocessor-based circuits or one or more DSP-based, FPGA-based, orASIC-based circuits, or any mix thereof. In a particular example, theprocessing circuitry 62 is specially adapted or otherwise configured tooperate according to the CN node method(s) disclosed herein, via theexecution of computer program instructions comprising a computer program66. The processing circuitry 62 may further use and or store variousitems of configuration data 68 associated with such operation, via thestorage 64.

The storage 64 comprises any one or more of solid-state storage, diskstorage, etc., and may provide both volatile, working memory andnon-volatile, program and data storage, and thus may include a mix ofmemory or storage circuit or device types. Non-limiting examples includeany one or more of SRAM, DRAM, FLASH, EEPROM, and Solid State Disk (SSD)storage.

In one or more embodiments the storage 64 includes a non-transitorycomputer-readable medium storing a computer program 66, the execution ofwhich by processing circuitry 62 in the CN node 24 configures theprocessing circuitry 62 according to the teachings herein.Non-transitory, as used here, does not necessarily mean permanent orunchanging, but does denote storage of at least some persistence.

FIG. 4 illustrates one embodiment of a method 400 of operation in a WD16 configured for operation in a wireless communication network 10. Themethod 400 includes receiving (Block 402) sidelink configurationinformation for a second cell 22-2 of the wireless communication network10, indicating sidelink resources and sidelink timing associated withthe second cell 22-2. Further, the method includes receiving (Block 404)handover signaling indicating a cellular handover of the wireless device16 from a first cell 22-1 of the wireless communication network 10 tothe second cell 22-2, and, in response: performing (Block 408) acellular handover process with respect to the second cell 22-2,including acquiring cellular synchronization with respect to the secondcell 22-2; and performing (Block 410) a sidelink synchronization processwith respect to the second cell 22-2, including acquiring sidelinktiming synchronization with respect to the second cell 22-2, andresuming or initiating sidelink communications using the sidelinkresources and the sidelink timing associated with the second cell 22-2,once sidelink synchronization is acquired with respect to the secondcell 22-2 via the sidelink synchronization process and irrespective ofwhether the cellular handover process has been completed. Note that ifhandover signaling is not received (NO from Block 404), the WD 16continues with ongoing operations (Block 406). Here, the first andsecond cells 22-1 and 22-2 may be “source” and “target” cells, as werediscussed in the context of FIG. 2.

In the handover context, resuming sidelink communications using thesidelink resources and the sidelink timing associated with the secondcell 22-2 comprises resuming sidelink communications that werepreviously performed according to the sidelink resources and sidelinktiming associated with the first cell 22-1. In an example embodiment orscenario, the sidelink timing in the second cell 22-2 uses a sidelinktiming reference that is different than a downlink timing reference usedfor cellular synchronization in the second cell 22-2. In such cases, thesidelink synchronization process uses the sidelink timing reference andthe cellular synchronization process uses the downlink timing reference.

In at least one case or embodiment, the sidelink timing reference in thesecond cell 22-2 comprises a GNSS timing reference, and the downlinktiming reference comprises one or more downlink synchronization signalstransmitted in the second cell 22-2, such as Primary SynchronizationSignals (PSS) and Secondary Synchronization Signals (SSS). The WD 16thus synchronizes with respect to the GNSS timing reference for sidelinkcommunications conducted using sidelink resources associated with thesecond cell 22-2, and synchronizes with respect to the downlinksynchronization signals for cellular communications conducted withrespect to the second cell 22-2.

In yet another embodiment or example case, receiving (Block 402) thesidelink configuration information for the second cell 22-2 comprisesreceiving the sidelink configuration information for the second cell22-2 via a cellular connection with the first cell 22-1. For example,the radio network node 20 associated with the first cell 22-1 providesthe sidelink configuration information for the second cell 22-2 inadvance of, or in conjunction with, handover of the WD 16 to the secondcell 22-2.

In a complementary example embodiment, a WD 16 is configured to carryout the method 400, or variations and extensions thereof. With momentaryreference back to FIG. 3, an example WD 16 includes communicationcircuitry 40 and processing circuitry 42. The communication circuitry 40is configured for communicating with radio network nodes 20 in thewireless communication network 10 via cellular connections and forcommunicating with other WDs 16 or nodes 70 via sidelink connections.Further, the processing circuitry 42 is operatively associated with thecommunication circuitry 40 and is configured to: receive sidelinkconfiguration information for a second cell 22-2 of the wirelesscommunication network 10, indicating sidelink resources and sidelinktiming associated with the second cell 22-2; receive handover signalingindicating a cellular handover of the wireless device 16 from a firstcell 22-1 of the wireless communication network 10 to the second cell22-2. The processing circuitry 42 is configured to respond to thehandover signaling by performing a cellular handover process withrespect to the second cell 22-2, including acquiring cellularsynchronization with respect to the second cell 22-2, and performing asidelink synchronization process with respect to the second cell 22-2.The sidelink synchronization process includes acquiring sidelink timingsynchronization with respect to the second cell 22-2. The WD 16 resumesor initiates sidelink communications using the sidelink resources andthe sidelink timing associated with the second cell 22-2, once sidelinksynchronization is acquired with respect to the second cell 22-2 via thesidelink synchronization process and irrespective of whether thecellular handover process has been completed.

As for complementary, network-side operations, FIG. 5 illustrates oneembodiment of a method 500 of operation at a radio network node 20configured for operation in a wireless communication network 10. Themethod 500 includes determining (Block 502) sidelink configurationinformation for a second cell 22-2 that neighbors a first cell 22-1provided by the radio network node 20. The sidelink configurationinformation indicates a sidelink resource configuration for the secondcell 22-2, and a sidelink synchronization configuration for the secondcell 22-2. In an example embodiment, the radio network node 20 obtainsthe sidelink configuration information based on receiving it fromanother radio network node 20, e.g., one that is associated with thesecond cell 22-2. In another alternative, the radio network node 20receives the sidelink configuration information from a node in the CN14.

In any case, the method 500 further includes the radio network node 20transmitting (Block 504) the sidelink configuration information to a WD16 having a cellular connection to the first cell 22-1. The transmissionof sidelink configuration information to the WD 16 occurs in advance of,or in conjunction with, a cellular handover of the WD 16 from the firstcell 22-1 to the second cell 22-2. The sidelink configurationinformation enables the WD 16 to acquire sidelink timing synchronizationwith respect to the second cell 22-2 using the indicated sidelinksynchronization configuration.

Transmitting (Block 504) the sidelink configuration information to theWD 16 comprises, for example, transmitting an indication that the secondcell 22-2 uses a sidelink timing reference that is different than adownlink timing reference used by the second cell 22-2. In the sameexample case or embodiment, or in another example case or embodiment,transmitting (Block 504) the sidelink configuration information to theWD 16 comprises the radio network node 20 transmitting an indicationthat the second cell 22-2 uses a GNSS timing reference for sidelinktiming. Such embodiments represent efficient mechanisms for providingthe WD 16 with enough information to obtain sidelink synchronizationwith respect to the second cell 22-2, while offering the advantages oflow signaling overhead.

In any case, the sidelink configuration information can be sent from theradio network node 20 to the WD 16 using, for example, RRC signaling.The information can be sent in advance of handover signaling sent by theradio network node 20 to the WD 16, or it can be sent in conjunctionwith such handover signaling. In at least one embodiment, the handoversignaling includes the sidelink configuration information. Further, inone or more embodiments, the radio network node 20 decides to transmitthe sidelink configuration information to the WD 16 responsive to atleast one of: a decision to initiate the cellular handover of the WD 16,and a determination that the WD 16 is likely to be handed over. As anexample of determining that the WD 16 is likely to be handed over, theradio network node 20 determines that the WD 16 is likely to be handedover as a function of any one or more of: a current location of the WD16, a direction of movement of the WD 16, and reception conditions atthe WD 16 with respect to one or more cells 22.

In a complementary example embodiment, a radio network node 20 isconfigured to carry out the method 500, or variations and extensionsthereof. With momentary reference back to FIG. 3, an example radionetwork node 20 is configured for operation in a wireless communicationnetwork 10 and comprises communication circuitry 30 and processingcircuitry 32. The communication circuitry 30 comprises receiver andtransmitter circuitry configured for communicating with wireless devicesand the processing circuitry 32 is operatively associated with thecommunication circuitry 30.

More particularly, the processing circuitry 32 is configured to: obtainsidelink configuration information for a second cell 22-2 of thewireless communication network 10 that neighbors a first cell 22-1provided by the radio network node 20. The sidelink configurationinformation indicates a sidelink resource configuration for the secondcell 22-2, and a sidelink synchronization configuration for the secondcell 22-2. The processing circuitry 32 is further configured to transmitthe sidelink configuration information to a WD 16 having a cellularconnection to the first cell 22-1. The transmission of the sidelinkconfiguration information occurs, in advance of, or in conjunction with,a cellular handover of the WD 16 from the first cell 22-1 to the secondcell 22-2. Such information enables the WD 16 to acquire sidelink timingsynchronization with respect to the second cell 22-2.

In one example, the processing circuitry 32 determines the sidelinkconfiguration information for the second cell 22-2, based on receivingsuch information, or related information, from another radio networknode 20, e.g., via inter-node communication interface signaling.Alternatively, the radio network node 20 receives such information froman OAM node, or other node in the CN 14. Further, in one example, theradio network node 20 sends the sidelink synchronization configurationinformation in the form of a flag, information element, or other dataitem that indicates the timing reference or base to be used by the WD 16for sidelink synchronization in the second cell 22-2. For example, theradio network node 20 sends an indication that the second cell 22-2 usesGNSS-based timing for sidelink communications.

While some examples herein involve V2X/ITS traffic using cellularnetwork resources, it will be appreciated that the teachings herein maybe applied to any traffic with similar characteristics. Further, toappreciate advantages attending the teachings herein, consider that a“legacy” or conventional cellular handover includes the following steps:(1) as part of the HO reconfiguration command message the source radionetwork node 20, e.g., an eNB, may signal a device-specific resourceconfiguration to be used in the target cell; (2) the WD 16, e.g., a UE,initiates the HO procedure and stops sidelink operation; (3) the UEobtains synchronization for the target cell and reads systeminformation; and (4) the UE resumes sidelink operation in the targetcell. Thus, conventionally, there is a certain, potentially significant,service interruption while the UE acquires synchronization and systeminformation for the target cell.

The teachings herein can be understood as “decoupling” the resumption ofsidelink communications from cellular handover process, and involvesproviding signaling to an appropriately configured UE. The signalingindicates sidelink timing and resources for a target cell, and enablesthe UE to synchronize to the target cell with respect to sidelinkcommunications and begin or resume sidelink communications usingtarget-cell resources, irrespective of whether the cellular handover ofthe UE to the target cell has completed.

The signaling to the UE includes, for example, the configuration ofsidelink resources to be used in the target cell. Common sidelinkresources that are not specific for a certain UE may be indicated insuch signaling. The signaling further includes synchronizationconfiguration to be used in the target cell. For example, differentcells (eNBs) may configure devices to prioritize differentsynchronization sources differently. In one example an eNB configuresUEs in its coverage to follow a certain UTC timing, derived e.g. fromGNSS signals. In another example an eNB configures UEs in its coverageto follow cellular timing, derived e.g. from downlink signals.

The above information needs to be exchanged among eNBs and potentiallyother NW nodes prior to the HO. Any protocol using any interface (e.g.,X2) may be used for such a purpose, including e.g. OAM or otherproprietary procedures in the radio network.

With respect to X2AP, an optional IE with assigned criticality “ignore”can be added to the LOAD INFORMATION message to convey the aboveinformation for one or more cells served by the sending eNB. The samecould also be achieved by using a private message instead of astandardized X2AP message.

It is worth noting, however, that synchronization configuration for acluster of eNBs is not likely to change frequently in time, so thebenefit of exchanging this type of information over a network interfacemay not be clear: coordination over OAM offers advantageous operation inthis respect.

A further aspect of the teachings herein, at least in some embodiments,is a new UE procedure for performing sidelink communication. Here,“sidelink communications” refers to any combination of transmissionand/or reception. In particular, after having received the RRC sidelinkreconfiguration described in the signaling above, the UE will: (1)acquire the synchronization reference according to theprotocol/priority/configuration indicated by the HO command message sentby source cell to UE and containing target cell information; and (2)initiate sidelink operation using the sidelink resources configurationfor the target cell, while still being served by the source cell.Sidelink resource configuration can include either a pool of resourcesto be autonomously selected by the UE or an eNB-selected resourceallocation.

Sidelink resources of the target cell can be used only for the durationof the handover, i.e. until triggeringRRCConnectionReconfigurationComplete or in case Radio Link Failure (RLF)is declared while performing handover. Alternatively, sidelink resourcescan be used further notification from target eNB (i.e. new resourceconfiguration provided either via dedicated signaling or dynamic grantson PDCCH), or in case RLF is declared. Such UE operations may berequired by standards implementation, or may be left for implementationas a proprietary feature.

One or more of the embodiments disclosed herein can be used by bothidle-mode and connected-mode UEs, for cell selection/reselection.Sidelink resources to be used in the target cell can also be acquiredvia broadcast signaling (e.g. System Information Block or SIBbroadcasting) from the source cell. Of course, not all embodiments mayuse such signaling. In embodiments that do, however, the SIB signalingof the source cell carries resource configuration to be used by the UE,at least until completion of cell selection/reselection procedure (forUEs in idle mode) or handover (for UEs in connected mode) or RLF (forUEs in connected mode).

Such SIB signaling can carry along with the resource configuration alsothe cell ID of the cell for which that resource configuration applies.The cell ID is supposed to be already known by the UE (e.g. from PSS/SSSacquisition). When the UE performs cell selection/reselection orhandover towards a target cell the corresponding resource configurationis used. Acquisition of resource configuration via SIB can be done bythe UE before handover triggering (e.g. after measurement reporttriggering) or before performing cell selection/reselection

In another embodiment, UE uses pre-configured resources when doinghandover or when doing cell selection/reselection. Usage ofpre-configured resources is triggered by the handover command or byinitiation of cell selection/reselection procedure.

With the above in mind, it will be appreciated that, similar toconsiderations associated with the Uu interface (the cellular link)between a UE and the cellular network, UEs engaged in PC5 communicationsare subject to latency when performing the handover. Looking at ProSeaccording to a conventional approach, a UE before continuing an ongoingPC5 session after handover command needs to wait for the target cellsending a D2D grant on PDCCH or dedicated signaling (if in connectedmode) indicating mode 1 and mode 2 resource allocation respectively.This disclosure presents various example methods and apparatuses foreliminating or at least substantially reducing PC5 service interruptionsassociated with cellular handover of UEs involved in PC5 communications.

For UEs in connected mode, target cell PC5 resources as well asinformation about synchronization configuration in the target cell canbe transferred via the (cellular) handover command. For example, if thetarget cell uses GNSS-based synchronization for sidelink, the UE maycontinue PC5 operations virtually without any interruption during thehandover operation. Thus, one solution presented herein involves thesignaling of the PC5 resources of the target cell, as well as the PC5synchronization configuration of the target cell, to the UE via thehandover command.

Such information also may be sent in advance of the handover command,e.g., responsive to determining that the handover decision has been madeor initiated, or responsive to determining that handover is likely. Inany case, the UE uses the signaled information to avoid or minimizeinterruption of sidelink operation during HO. At least in cases wherethe source and target cell use the same GNSS synchronization reference,signaling an indication of such to the UE may allow the UE to avoidinterruptions in sidelink communications in association with beinghanded over from the source cell to the target cell. In other words, oneexample of signaling sidelink synchronization configuration informationfor a target cell to a UE comprises sending an indication to the UE thatthe target cell uses the same timing reference or base for sidelinkcommunications as is used in the source cell. More broadly, transmittingthe sidelink synchronization configuration information to the UE for thetarget cell may comprise sending a flag, information element, or otherindicator, indicating the timing reference for synchronization ofsidelink communications when using resources in the target cell.

Notably, modifications and other embodiments of the disclosedinvention(s) will come to mind to one skilled in the art having thebenefit of the teachings presented in the foregoing descriptions and theassociated drawings. Therefore, it is to be understood that theinvention(s) is/are not to be limited to the specific embodimentsdisclosed and that modifications and other embodiments are intended tobe included within the scope of this disclosure. Although specific termsmay be employed herein, they are used in a generic and descriptive senseonly and not for purposes of limitation.

ABBREVIATIONS

3G Third Generation of Mobile Telecommunications Technology

BSM Basic Safety Message

BW Bandwidth

CAM Cooperative Awareness Message

DPTF Data Packet Transmission Format

D2D Device-to-Device Communication

DENM Decentralized Environmental Notification Message

DSRC Dedicated Short-Range Communications

eNB eNodeB

ETSI European Telecommunications Standards Institute

LTE Long-Term Evolution

NW Network

RS Reference Signals

TF Transport Format

SAE Society of the Automotive Engineers

UE User Equipment

V2I Vehicle-to-Infrastructure

V2P Vehicle-to-Pedestrian

V2V Vehicle-to-vehicle communication

V2x Vehicle-to-anything-you-can-imagine

wrt with respect to

SPS Semi Persistent Scheduling

DMRS Demodulation reference signals

OCC Orthogonal cover code

HO Handover

SIB System Information Block

RLF Radio Link Failure

3GPP Third Generation Partnership Project

RRC Radio Resource Control

PDCCH Physical Downlink Control Channel

PSS Primary Synchronization Signal

SSS Secondary Synchronization Signal

What is claimed is:
 1. A method of operation in a wireless deviceconfigured for operation in a wireless communication network, the methodcomprising: receiving sidelink configuration information for a secondcell of the wireless communication network, indicating sidelinkresources and sidelink timing associated with the second cell; receivinghandover signaling indicating a cellular handover of the wireless devicefrom a first cell of the wireless communication network to the secondcell, and, in response: performing a cellular handover process withrespect to the second cell, including acquiring cellular synchronizationwith respect to the second cell; and performing a sidelinksynchronization process with respect to the second cell, includingacquiring sidelink timing synchronization with respect to the secondcell, and resuming or initiating sidelink communications using thesidelink resources and the sidelink timing associated with the secondcell, once sidelink synchronization is acquired with respect to thesecond cell via the sidelink synchronization process and irrespective ofwhether the cellular handover process has been completed; and whereinthe sidelink timing associated with the second cell uses a sidelinktiming reference that is different than a downlink timing reference usedfor the cellular synchronization with respect to the second cell, andwherein the sidelink synchronization process uses the sidelink timingreference and the cellular synchronization process uses the downlinktiming reference.
 2. The method of claim 1, wherein resuming orinitiating the sidelink communications using the sidelink resources andthe sidelink timing associated with the second cell comprises resumingsidelink communications previously performed according to sidelinkresources and sidelink timing associated with the first cell.
 3. Themethod of claim 1, wherein the sidelink timing reference comprises aGlobal Navigation Satellite System (GNSS) timing reference, and whereinthe downlink timing reference comprises one or more downlinksynchronization signals transmitted in the second cell.
 4. The method ofclaim 1, wherein the receiving the sidelink configuration informationfor the second cell comprises receiving the sidelink configurationinformation for the second cell via a cellular connection with the firstcell.
 5. A wireless device configured for operation in a wirelesscommunication network, the wireless device comprising: communicationcircuitry configured for communicating with radio network nodes in thewireless communication network via cellular connections and forcommunicating with other wireless devices or nodes via sidelinkconnections; and processing circuitry operatively associated with thecommunication circuitry and configured to: receive sidelinkconfiguration information for a second cell of the wirelesscommunication network, indicating sidelink resources and sidelink timingassociated with the second cell; receive handover signaling indicating acellular handover of the wireless device from a first cell of thewireless communication network to the second cell, and, in response:perform a cellular handover process with respect to the second cell,including acquiring cellular synchronization with respect to the secondcell; and perform a sidelink synchronization process with respect to thesecond cell, including acquiring sidelink timing synchronization withrespect to the second cell, and resume or initiate sidelinkcommunications using the sidelink resources and the sidelink timingassociated with the second cell, once sidelink synchronization isacquired with respect to the second cell via the sidelinksynchronization process and irrespective of whether the cellularhandover process has been completed; and wherein the sidelink timingassociated with the second cell uses a sidelink timing reference that isdifferent than a downlink timing reference used for the cellularsynchronization with respect to the second cell, and wherein theprocessing circuitry is configured to perform the sidelinksynchronization process using the sidelink timing reference, and performthe cellular synchronization process using the downlink timingreference.
 6. The wireless device of claim 5, wherein the processingcircuitry is configured to perform the sidelink communications accordingto sidelink timing and sidelink resources associated with the first cellin advance of receiving the handover signaling, and to resume thesidelink communications according to the sidelink timing and sidelinkresources associated with the second cell.
 7. The wireless device ofclaim 5, wherein the sidelink timing reference comprises a GlobalNavigation Satellite System (GNSS) timing reference, and wherein thedownlink timing reference comprises one or more downlink synchronizationsignals transmitted in the second cell.
 8. The wireless device of claim5, wherein the processing circuitry is configured to receive thesidelink configuration information for the second cell via a cellularconnection of the wireless device with the first cell.
 9. Anon-transitory computer readable medium storing a computer programcomprising instructions that, when executed by at least one processor ofa wireless device configured for operation in a wireless communicationnetwork, causes the wireless device to: receive sidelink configurationinformation for a second cell of the wireless communication network,indicating sidelink resources and sidelink timing associated with thesecond cell; receive handover signaling indicating a cellular handoverof the wireless device from a first cell of the wireless communicationnetwork to the second cell, and, in response: perform a cellularhandover process with respect to the second cell, including acquiringcellular synchronization with respect to the second cell; and perform asidelink synchronization process with respect to the second cell,including acquiring sidelink timing synchronization with respect to thesecond cell, and resume or initiate sidelink communications using thesidelink resources and the sidelink timing associated with the secondcell, once sidelink synchronization is acquired with respect to thesecond cell via the sidelink synchronization process and irrespective ofwhether the cellular handover process has been completed; and whereinthe sidelink timing associated with the second cell uses a sidelinktiming reference that is different than a downlink timing reference usedfor the cellular synchronization with respect to the second cell, andwherein the processing circuitry is configured to perform the sidelinksynchronization process using the sidelink timing reference, and performthe cellular synchronization process using the downlink timingreference.